2018 USGS Lidar DEM: Bayou Nezpique, LA

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Bulk download of data files in GeoTIFF format in geographic coordinates and orthometric heights in meters.

Link to data set breaklines.

The Data Access Viewer (DAV) allows a user to search for and download elevation, imagery, and land cover data for the coastal U.S. and its territories. The data, hosted by the NOAA Office for Coastal Management, can be customized and requested for free download through a checkout interface. An email provides a link to the customized data, while the original data set is available through a link within the viewer.

This graphic displays the footprint for this lidar data set.

Link to data set report.

This data source was used (along with the airborne GPS/IMU Data) to georeference the lidar point cloud data; additionally, a subset of the collected surveyed data points were used solely as independent ground control to assess the accuracy of the lidar point cloud.

This data source, once calibrated and georeferenced, resulted in the point cloud from which the derivative deliverable products were produced.

Florabama Geospatial Solutions (FGS) collected 284 check points (98 Control, 102 NVA, 84 VVA) in different classifications spread throughout the project area. The control point coordinate values for this project are referenced to National Geodetic Survey (NGS) control monuments in the National Spatial Reference System (NSRS). Horizontal datum is referenced to UTM, NAD1983, Zone 15 North. Vertical values represent the North American Vertical Datum of 1988 (NAVD88). GEOID 12B was used to translate the ellipsoid heights to orthometric heights. FGS used LSU C4G Real Time Network Data Correction Service to determine coordinate values for the survey control points and logged raw data at the rovers for post-processing. FGS also observed static data on 10 base station sites spread evenly throughout the project area. All site calibration points were oberved for at least ten (10) minutes and all LiDAR control points were observed for at least six (6) minutes. A site calibration was performed using the data that was collected via LSU C4G RTN. Existing control throughout and surrounding the project area were evaluated against published values and OPUS solutions held as fixed control. The site calibration was performed using Trimble Business Center Software.

Firstly, the individual lidar mission points in Leica raw scan format were output to ASPRS LAS format using Leica Cloud Pro software, initially using as default values those resulting from the last successfully calibrated mission for the lidar scanner system. Subsequently, Bayes StripAlign software (version 2.04B) was utilized for LiDAR calibration, assessment of calibration validity, and assessment of point cloud alignment to control. If a calibration error greater than allowable according to project specifications is observed within a mission, the roll, pitch and scanner scale corrections that need to be applied to refine the calibration are calculated and the mission in question is reprocessed and re-validated. Additionally, data collected by the lidar unit is reviewed for completeness, acceptable density, and to make sure all data is captured without errors or corrupted values.

The raw point cloud was segmented into a contiguous set of 1,000 meter x 1,000 meter tiles based on the U.S. National Grid tiling and naming scheme. After tiling, Terrasolid TerraScan software ground classification routines were run to generate an initial point classification, primarily identifying ground and noise. Subsequent to automated classification, manual review and edit of point classifications was performed to meet project classification specifications. The point classifications used are as follows: 1 - Processed, but unclassified; 2 - Bare-earth ground; 7 - Low Noise; 9 - Water; 10 - Ignored Ground (Breakline Proximity); 17 - Bridge Decks; and, 18 - High Noise. Concurrently with manual point classification, heads-up digitizing of 2D hydro-flattening breaklines of inland streams and rivers with a 100 foot nominal width as well as inland ponds and lakes of 2 acres or greater surface area was performed. Breakline elevation values were then derived from the point cloud and assigned to all inland ponds and lakes, inland pond and lake islands, and inland stream and river islands using TerraModeler functionality. Elevation values were assigned to all inland streams and rivers using TerraScan. All ground (ASPRS Class 2) lidar data falling within the collected inland water body breaklines were then classified as water (ASPRS Class 9) using TerraScan macro functionality. A buffer of 0.3 meters was used around each hydro-flattened feature to de-conflict discreet breakline vertices and segments from lidar ground returns; this was accomplished by reclassifying the ground points within the buffer to Ignored Ground (ASPRS Class 10). LAStools software was used to perform final statistical analysis of the classes in the LAS files, on a per tile level to verify final classification metrics as well as completeness and validity of LAS header information.

Triangulated Irregular Network (TIN) surface models were used within the Terrasolid TerraScan and TerraModeler softwares to heads-up digitize 2D breaklines of inland streams and rivers with a 100 foot nominal width as well as inland ponds and lakes of 2 acres or greater surface area. Elevation values were then derived from the TIN and assigned to all inland ponds and lakes, inland pond and lake islands, and inland stream and river islands using TerraModeler functionality. Elevation values were assigned to all inland streams and rivers using TerraScan. All ground (ASPRS Class 2) lidar data falling within the collected inland water body breaklines were then classified as water (ASPRS Class 9) using TerraScan macro functionality. A buffer of 0.3 meters was also used around each hydro-flattened feature to de-conflict discreet breakline vertices from lidar ground returns; this was accomplished by reclassifying the ground points within the buffer to Ignored Ground (ASPRS Class 10). The breakline files were then translated to ESRI File-Geodatabase format using ESRI conversion tools. Breaklines are reviewed against lidar intensity imagery to verify completeness of capture. All breaklines are then compared to TINs created from ground only points. The horizontal placement of breaklines is compared to terrain features and the breakline elevations are compared to lidar elevations to ensure all breaklines match the lidar within acceptable tolerances. Some deviation is expected between breakline and lidar elevations due to monotonicity, connectivity, and flattening rules that are enforced on the breaklines. Once completeness, horizontal placement, and vertical variance is reviewed, all breaklines are reviewed for topological consistency and data integrity using a combination of ESRI Data Reviewer tools and proprietary tools.

Class 2 (ground) lidar points in conjunction with the hydro-flattening breaklines were used to create a 0.5 meter hydro-flattened Raster DEM. Using automated scripting routines within ArcMap, an ERDAS Imagine IMG file was created for each tile. Each surface is reviewed using ArcGIS to check for any surface anomalies or incorrect elevations found within the surface.

The NOAA Office for Coastal Management (OCM) created references to the USGS GeoTIFF files that were ingested into the NOAA Digital Coast Data Access Viewer (DAV). No changes were made to the data. The DAV will access the raster data as it resides on Amazon Web Services (AWS).

These are the GeoTIFF files that are being accessed:

https://prd-tnm.s3.amazonaws.com/index.html?prefix=StagedProducts/Elevation/OPR/Projects/LA_Bayou_Nezpique_B1_2018/TIFF/

https://prd-tnm.s3.amazonaws.com/index.html?prefix=StagedProducts/Elevation/OPR/Projects/LA_Bayou_Nezpique_B2_2018/TIFF/

https://prd-tnm.s3.amazonaws.com/index.html?prefix=StagedProducts/Elevation/OPR/Projects/LA_Bayou_Nezpique_B3_2018/TIFF/

https://prd-tnm.s3.amazonaws.com/index.html?prefix=StagedProducts/Elevation/OPR/Projects/LA_Bayou_Nezpique_B4_2018/TIFF/

https://prd-tnm.s3.amazonaws.com/index.html?prefix=StagedProducts/Elevation/OPR/Projects/LA_Bayou_Nezpique_B5_2018/TIFF/

https://prd-tnm.s3.amazonaws.com/index.html?prefix=StagedProducts/Elevation/OPR/Projects/LA_Bayou_Nezpique_B6_2018/TIFF/

https://prd-tnm.s3.amazonaws.com/index.html?prefix=StagedProducts/Elevation/OPR/Projects/LA_Bayou_Nezpique_2018_D18/LA_Bayou_Nezpique_TL_2018/TIFF/